Polymer modified asphalt for paving applications and methods for preparing various polymer modified asphalt compositions are well known in the art. Various polymers, including diene elastomers such as polybutadiene, EPDM, EPR and styrenic block copolymers (SBCs) such as styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SIS) block copolymers, are commonly combined with bitumen to improve the performance of the bitumen. See, for example, U.S. Pat. No. 5,190,998 and U.S. Pat. No. 6,150,439. It is well known in the art to utilize styrenic block copolymers to improve the performance of bitumen. The degree to which property improvements are realized depends upon the compatibility of the block copolymer and the bitumen. Highly compatible or compatibilized polymers are most effective in providing property improvements. Over the years, researchers have developed a range of chemical techniques to improve the compatibility of these types of polymers with bitumens. An extensive range of additives have been used for the purpose of “curing” or “crosslinking” the polymers and bitumens thereby rendering the mixture compatible. These additions include sulfur crosslinking agents and sulfur-containing crosslinking agents. Sulfur has long been known to be added to polymer modified bitumens to strengthen and accelerate the polymer-bitumen bonding and curing process. See, for example, U.S. Pat. No. 4,145,322 and U.S. Pat. No. 4,242,246. While sulfur itself is relatively safe, the reaction between sulfur, the block copolymers and asphalt generates hydrogen sulfide (H2S) which is extremely hazardous. Accordingly, from an environmental and safety standpoint, there is a strong desire to eliminate sulfur and sulfur containing crosslinking agents which aid in the curing of bituminous formulations.
In addition, there are improvements associated with the use of styrenic block copolymers which the bitumen paving industry would like to see. These improvements include, but are not limited to, improved mixing, shorter cure times, less separation with incompatible asphalts, and increased efficiency.
Bituminous compositions containing block copolymer compositions having a high vinyl content or block copolymer compositions having a high vinyl content and a low diblock content have been used in an attempt to provide bituminous compositions with better properties. See, for example, U.S. Pat. No. 4,530,652, U.S. Pat. No. 5,798,401, U.S. Pat. No. 5,854,335, and U.S. Pat. No. 6,508,875. Compositions high in diblock have also been used to prepare bituminous compositions in an effort to provide rapid and easy mixing and to improve dispersion. See, for example, U.S. Patent Publication No. 2005/0137295 and U.S. Patent Publication No. 2005/0004273.
While many formulations have attempted to overcome one or more of these issues, many fail or only address a small number of the issues. There still exists a need for an improved process for preparing polymer-modified bituminous binder compositions using existing asphalt facilities while maximizing properties and minimizing many of the environmental and safety concerns associated with such processes. Ideally, such a process would provide ready mixing, produce a product that is stable in storage, and result in a quick cure of polymer and bitumen.